Balancing accuracy, efficiency, and flexibility in radiation
calculations for dynamical models
Abstract
This paper describes the initial implementation of a new toolbox that
seeks to balance accuracy, efficiency, and flexibility in radiation
calculations for dynamical models. The toolbox consists of two related
code bases: Radiative Transfer for Energetics (RTE), which computes
fluxes given a radiative transfer problem defined in terms of optical
properties, boundary conditions and source functions, and RRTM for GCM
applications - Parallel (RRTMGP), which combines data and algorithms to
map a physical description of the gaseous atmosphere into such a
radiative transfer problem. The toolbox is an implementation of
well-established ideas, including the use of a k-distribution to
represent the spectral variation of absorption by gases and the use of
two-stream, plane-parallel methods for solving the radiative transfer
equation. The focus is instead on accuracy, by basing the k-distribution
on state-of-the-art spectroscopy, and on the sometimes-conflicting goals
of flexibility and efficiency. Flexibility is facilitated by making
extensive use of computational objects encompassing code and data, the
latter provisioned at run time and potentially tailored to specific
problems. The computational objects provide robust access to a set of
high-efficiency computational kernels that can be adapted to new
computational environments. Accuracy is obtained by careful choice of
algorithms and through tuning and validation of the k-distribution
against benchmark calculations. Flexibility with respect to the host
model implies user responsibility for maps between clouds and aerosols
and the radiative transfer problem, although comprehensive examples are
provided for clouds.